The process industry employs process variable transmitters to monitor process variables associated with substances such as solids, slurries, liquids, vapors, and gasses in chemical, pulp, petroleum, pharmaceutical, food and other processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. A process fluid temperature transmitter provides an output related to a sensed process fluid temperature. The temperature transmitter output can be communicated over a process communication loop to a control room, or the output can be communicated to another process device such that the process can be monitored and controlled. In order to monitor a process fluid temperature, the transmitter includes or is coupled to a sensor, such as a resistance temperature device (RTD) or thermocouple.
One specific type of temperature transmitter is known as a head-mount temperature transmitter. Such a transmitter generally includes a connection head or junction box that is ruggedized for exposure to harsh environments. The connection head can be designed in accordance with the criteria of current DIN standard 43 729 Form B. Such design is relatively smaller than other process variable transmitter enclosures. The smaller design facilitates transmitter mounting in crowded installation environments. Further, the smaller design also provides a smaller mass coupled to the sensor probe. Such mass reduction reduces the possibility of vibration damage occurring in the transmitter.
The connection head or junction box can be explosion-proof in conformance with NEC Sections 500-503, dated 1996. Typically, an electronics module is placed within the connection head and mounted with fasteners to provide a transmitter that is highly modular. Such modularity facilitates transmitter configuration changes as well as maintenance. An example of such a head-mount temperature transmitter is the Model 248 Temperature Transmitter available from Rosemount Inc. of Chanhassen, Minn.
Another specific type of temperature transmitter is known as a rail-mount temperature transmitter. A rail-mount temperature transmitter may include many of the same electronics as a head-mount temperature transmitter, but is configured to be mounted directly to a wall or a DIN rail.
A third specific type of temperature transmitter is generally specified for very high accuracy applications and/or environments that provide an electromagnetic interference challenge. In such situations, a dual-compartment, explosion proof housing is provided. Typically the field wiring for the process communication loop conductors and sensor wires are provided in the first compartment and the transmitter electronics are provided in a second compartment. This approach achieves the necessary robustness to the environment by utilizing the dual-compartment in order to isolate the field wiring from the measurement electronics via an EMI (electromagnetic interference) filter positioned between the first and second compartments. In some cases, no filter is used and conductors simply pass through a feedthrough between the first and second compartments While a dual-compartment temperature transmitter typically requires additional cost, the cost is offset by the extreme robustness and/or accuracy provided by the device.
The provision of three distinct types of temperature transmitters generally requires a consumer to pick one specific type and accept the various advantages/disadvantages of the performance and/or cost of the selected type. Providing a temperature transmitter product offering that could potentially bridge some of the distinct types of applications and cost requirements would allow consumers to select products with a potentially better fit for their particular applications.